A vacuum ultraviolet photolysis of ethyl bromide at 174.3-174.5 nm was studied over the pressure range of 0.2-38.2 torr at room temperature using a nitrogen resonance lamp.
The pressure effect with and without He as an additive was investigated. A scavenger effect of the reaction was also observed by adding NO as a radical scavenger.
The principal reaction products were $C_2H_4$, $C_2H_6$ and $CH_3CHBr_2$. Increasing pressure without He the product quantum yields, Φ, of $C_2H_4$ and $CH_3CHBr_2$ remain constant, while that of $C_2H_6$ was found to be weak positive pressure dependence. When the pressure of He was varied at a constant pressure of $C_2H_5Br$, however, the quantum yields of all products were found to be pressure independence. Addition of NO completely suppressed the formation of $C_2H_6$ and $CH_3CHBr_2$, and partially reduced that of $C_2H_4$. These results were interpreted in terms of two channel competition between the molecular eliminations and the formation of radicals. Two different decomposition modes were 20% molecular elimination and 80% radical reactions, respectively.
From the aforementioned results, it is suggested that there exist two electronically excited states and that reactant molecule which absorbs a photon proceeds to any one of two different electronically excited states through one of two pathways. One of the electronically formed excited states plays a role as the main source of the molecular elimination products and the other state goes on the radical decomposition modes.
174.3-174.5nm 의 광을 내는 질소 공명 램프를 이용하여 에틸브로마이드의 광분해 반응을 0.2-38.2Torr 의 시료 압력 범위에서 행하였다. 또한 반응 생성물 분포에 대한 압력 효과와 스케빈져 효과를 면밀히 분석하였다. 주 생성물로 $CH_2=CH_2,C_2H_6$ 그리고 $CH_3CHBr_2$가 확인됐다. 헬륨 반응물의 압력을 변화시키면서 조사한 결과는 $C_2H_6$ 의 생성양이 약간 증가 하였으나 헬륨의 압력을 변화시키면서 행한 실험에서는 반응 생성물의 양이 일정한 것으로 나타났다. 라디칼 스케빈져로서 NO를 첨가했을 때는 오직 $CH_2=CH_2$ 만 생성되었다.
이러한 결과에 의해 에틸 브로마이드의 광분해 반응에는 두 가지 들뜬 상태가 존재함을 알았고 광을 흡수한 두 가지 경로를 통해 두 개의 다른 들뜬 상태중에 어떤 하나로 전이가 일어난다. 이렇게 형성 된 들뜬 상태에서 하나는HBr 분자 이탈 반응을 일으키고 다른 들뜬 상태는 탄소와 브롬 사이의 결합을 끊는 반응으로 진행된다. 이와 같이 두 가지 들뜬 상태는 분자 이탈 반응 20%와 라디칼 생성 반응 80%를 생성하게 되는 것을 알았다.
